Contact printing using high volume presses is commonly employed to print a large number of copies of an image. Contact printing presses utilize printing plates to apply colorants to a surface to form an image thereon. The surface can form part of a receiver medium (e.g. paper) or can form part of an intermediate component adapted to transfer the colorant from its surface to the receiver medium (e.g. a blanket cylinder of a press). In either case, a colorant pattern is transferred to the receiver medium to form an image on the receiver medium.
Printing plates typically undergo various processes to render them in a suitable configuration for use in a printing press. For example, exposure processes are used to form images on an imageable surface of a printing plate that has been suitably treated so as to be sensitive to light or heat radiation. One type of exposure process employs film masks. The masks are typically formed by exposing highly sensitive film media using a laser printer known as an “image-setter.” The film media can be additionally developed to form the mask. The film mask is then placed in area contact with a sensitized printing plate, which is in turn exposed through the mask. Printing plates exposed in this manner are typically referred to as “conventional printing plates.” Typical conventional lithographic printing plates are sensitive to radiation in the ultraviolet region of the light spectrum.
Another conventional method exposes printing plates directly through the use of a specialized imaging apparatus typically referred to as a plate-setter. A plate-setter, in combination with a controller that receives and conditions image data for use by the plate-setter, is commonly known as a “computer-to-plate” or “CTP” system. CTP systems offer a substantial advantage over image-setters in that they eliminate film masks and associated process variations associated therewith. Printing plates imaged by CTP systems are typically referred to as “digital” printing plates. Digital printing plates can include photopolymer coatings (i.e. visible light plates) or thermo-sensitive coatings (i.e. thermal plates).
Many types of printing plates also undergo additional processing steps which can include chemical development. For example, chemical development steps are additionally required to amplify a difference between exposed and un-exposed areas. Other processing steps can include pre-heating and/or post heating steps. Once exposed or imaged, some printing plates undergo a pre-heating process so as to change the solubility of various regions of the printing plate in a subsequent chemical development process to achieve the desired differentiation between printable and non-printable areas. Post-baking of a chemically developed printing plate can be conducted to impart various desired characteristics to the printing plate. Such characteristics can include increased plate life. Gumming processes can also be performed to protect various surfaces of the printing plate from adverse environmental conditions. Further processing steps can include punching and bending procedures which can be used to impart various features on the printing plates to facilitate the mounting and registration of the printing plates on press. In some cases, some CTP systems include on-board punching capabilities.
The various processing steps are typically conducted within a processing line made up of various systems. FIGS. 1A, 1B, and 1C each show a schematic plan and side views illustrating example conventional processing lines 102A, 102B, and 102C. Processing lines 102A, 102B, and 102C are each examples of typical processing lines that can be used to process various printing plates 24 ejected from an imaging apparatus 100 such as a CTP system. The choice of a particular processing line configuration can be dependant on various factors which can include the type of printing plates 24 to be imaged, the space available to accommodate the processing line and a desire to marry a particular printing plate 24 with a particular system within the processing line. Such a marriage may arise when a vendor bundles both the printing plates 24 and various processing line systems to create an economic opportunity that is beneficial for the customer.
Each of the processing lines 102A, 102B, and 102C include various systems. Various apparatus can be employed to guide the printing plates 24 through various process paths to, or among the various systems of a given processing line. Apparatus which can include various conveyors (e.g. belt, roller, or chain conveyors), gantries and the like can be used to transport the printing plates 24 between the various systems and present the plates at a given system with a positioning suitable for the particular processing associated with that system. In some cases, the apparatus are part of a processing line system.
Processing lines 102A and 102B each include various systems that include a pre-bake oven 110, a chemical developer 112, and a post-bake oven 114. Processing line 102C includes a chemical developer 116 and post-bake oven 114. Each of the processing lines 102A, 102B, and 102C terminates with a plate stacker system 115. It is understood that each of the processing lines are exemplary in nature and other processing lines can use other combinations or types of systems.
The configuration of the each of the systems can dictate how each of the printing plates 24 is processed within the systems as well as the overall throughput of the processing line. In these illustrated cases, each of these systems processes the printing plates 24 as the plates are moved through them. Accordingly, suitable processing of the printing plates 24 is typically dependant on a rate of movement of the printing plates 24 through a system of the processing line. In some cases, a rate of movement of a printing plate 24 through a first system may be adjusted according to a rate of movement of the printing plate 24 required by an additional system.
Other aspects of the particular configuration of a particular system can impact the overall throughput of an associated processing line. Typically, most pre-bake ovens are conveyor ovens. Examples of conveyor ovens adapted to heat printing plates are described in U.S. Pat. No. 5,964,044 (Lauerdorf et al.) and in U.S. Pat. No. 6,323,462 (Strand). In this regard, pre-bake oven 110 comprises a movable support 120 adapted to transport a printing plate 24 through the oven with a desired rate of movement. Needless to say, movable support 120 must be suitably constructed to withstand the oven temperatures. In various pre-bake ovens, movable support 120 typically takes the form of a conveyor that includes an endless loop of a meshed material 122 that is driven by various sprockets 124. Meshed material 122 is selected to withstand the oven temperatures and can include metals such a steel or stainless steel, for example.
The meshed movable support 120 can be used to better support the printing plate as it is transported through pre-bake oven 110. Problems can however arise with this configuration of pre-bake oven 110. For example, when pre-bake oven 110 is the first processing system in its associated processing line, care must be taken as printing plates 24 are transferred from imaging apparatus 100 to pre-bake oven 110. A printing plate 24 should not be ejected from imaging apparatus 100 with a rate of movement that is substantially greater than that of meshed movable support 120. To do so would increase a probability that an edge portion or corner portion of the printing plate 24 would be caught in the mesh and result in damage to the printing plate 24. Accordingly, it is typically desired that printing plates 24 be ejected from imaging apparatus 100 with a rate of movement that is substantially similar to the rate of movement of the meshed moveable support 120.
Some processing lines attempt to reduce similar potential damage to printing plates by introducing a buffering system. For example, processing line 102B includes a buffering system 118 in a location between imaging apparatus 100 and pre-bake oven 110. In this conventional processing line, buffering system 118 also includes a moveable support 126 which is adapted to transport a printing plate 24 ejected from imaging apparatus 100 towards pre-bake oven 110. In this case, movable support 126 forms part of a conveyor and includes a plurality of belts 127 that are driven by plurality of drive pulleys 128. Since movable support 126 is separated from the heated components of pre-bake oven 110, belts 127 need not be constrained to incorporate various heat resistant materials that are typically employed in conveyor oven applications. Belts 127 can include suitable elastomeric, plastic or metal compositions for example. Typically, belts 127 have frictional characteristics suitable for engaging a surface of a printing plate 24 to transport the printing plate. These frictional characteristics can also be tempered to allow relative movement, or slip to occur between the belts 127 and a printing plate 24 as the plate is ejected from the imaging apparatus 100 onto the belts 127. For example, belts 127 can be driven at a speed that is substantially the same as that of the meshed movable support 120 of pre-bake oven 110 to reduce the potential damage to a printing plate 24 transferred between the two systems. The printing plate 24 can, however, be ejected from imaging apparatus 100 at a much faster speed than that of belts 127 since their construction allows for slippage as the moving printing plate 24 is ejected onto the moving belts 127. This processing line configuration allows increased throughput conditions but at a cost of additional space requirements needed to accommodate buffering system 118. The belted configuration of movable support 126 reduces the likelihood of damaging a printing plate ejected thereon even at increased speeds. Other buffering systems can use other forms of movable supports including supports made up of a series of driven rollers.
Processing line 102C does not include a pre-bake oven. Rather printing plates 24 are directly transferred from imaging apparatus 100 to chemical developer 116. Chemical developer 116 includes various moveable members adapted to receive a printing plate 24 ejected from imaging apparatus 100 and transport the printing plate within chemical developer 116. In this case, chemical developer includes a support roller 129A and a nip roller 129B. Both support roller 129A and nip roller 129B are adapted to move in a rotational manner. At least one of support roller 129A and nip roller 129B can be driven members. In this processing line configuration, a printing plate 24 is typically introduced into support roller 129A and nip roller 129B with a speed that does not substantially exceed the speed with which the rollers transport the printing plate within chemical developer 116. Increased ejection speeds could cause buckling in the printing plate 24.
It now becomes apparent to those skilled in the art that the final throughput of the entire plate making process can vary according to the configuration of a particular processing line employed to process the printing plates 24. The processing speed of a processing line is typically dependent on the particular configuration of a system within the processing line.
Conventional CTP systems have employed various printing plate ejection systems. Some conventional CTP ejection systems eject a sequence of printing plates 24 according to a fixed minimum ejection time parameter. For example, one conventional method involves operating an ejector to engage a surface of a first printing plate 24 and move the printing plate 24 to eject it from the CTP system. Each of the printing plates 24 is ejected with a common speed that substantially matches a speed of a processing line that is fed by the CTP system. A printing plate 24 is continuously engaged by the ejector until the ejector reaches an end-of-travel position that is a common position for the ejection of each of the printing plates 24. If a next printing plate 24 is ready to be ejected, the conventional ejection method waits until a set amount of time related to the fixed minimum ejection time parameter had elapsed and then starts ejecting the next printing plate 24 with the common ejection speed. If the ejection readiness of the next printing plate 24 exceeds a time related to the fixed minimum ejection time parameter, then the next printing plate 24 is ejected when ready without waiting, but still with the common ejection speed. This ejection speed does not allow the next printing plate 24 to catch up to the previously ejected printing plate 24, thereby adversely impacting the throughput.
Even if the next printing plate 24 is ready to be ejected, variances in the spacing between these conventionally ejected printing plates 24 can arise. Each printing plate 24 is ejected by operating the ejector to engage a surface of the printing plate 24 prior to moving the plate. The surfaces of the printing plates 24 engaged by these conventional ejection systems correspond to common regions of each of the printing plates 24. For example, the engaged surfaces can be common edge surfaces such as common trailing edge surface or common leading edge surfaces of the printing plates 24 (i.e. as referenced with a direction of movement of the ejection path the printing plates 24 are moved along). The surfaces can be engaged at a common distance from a common reference of each printing plate 24 (i.e. a common leading or trailing edge). FIG. 2 shows sequence of printing plates 24 ejected by this conventional ejection method. In this case each of the printing plates 24 are ejected along a path 135 by causing the ejection system (not shown) to engage a printing plate trailing edge 130 (i.e. also known as the “tail”) during the ejection process. When each of the printing plates 24 is available for ejection, the conventional use of the minimum ejection time parameter results in a common tail-to-tail positioning between each adjacent printing plates 24 in the sequence of ejected printing plates. However, since each of the printing plates 24 can include a different size at least along a direction of ejection path 135, a spacing between the tail of each printing plate 24 and the leading edge 132 of printing plate (i.e. also known as the “tip”) of an adjacent printing plate 24 causes variable tail-to-tip spacing between various printing plates 24 in the sequence. Variable tail-to-tip spacing can deviate from a desired tail-to-tip spacing required by a particular processing line and thereby adversely impact the throughput of the processing line.
In view of the limitations in the prior art there is a need for an imaging apparatus with improved plate handling capabilities. There is also a need for an imaging apparatus adapted to improve the transfer of printing plates between various supports.